Merrill, Michigan Weather Forecast Discussion

216
FXUS63 KDTX 222000
AFDDTX
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
400 PM EDT Mon Sep 22 2025
.KEY MESSAGES...
- Scattered showers and thunderstorms will be possible through the
middle of the week. Localized heavy rainfall may be possible.
- Temperatures in the 70s throughout the week which will generally
be at to slightly above normal.
&&
.DISCUSSION...
Southeast Michigan holding position late this afternoon within the
southern expanse of broad mid level troughing emanating from a
closed low migrating across lake Superior. Underlying low level
environment remains characterized as moist and weakly unstable, as
daytime heating works to lift afternoon temps into the 70s. A more
noteworthy gradient in instability emerging as early day convective
activity across areas generally south of I-69 effectively limits the
degree of destabilization across the corridor, while points north
push toward 700-1000 j/kg of mlcape. While the overall forcing field
remains rather nebulous, a more focused corridor of ascent emerging
across central lower mi as shortwave filaments pivot through the mid
level cyclonic periphery. This ascent evident with ongoing activity
lifting across west-central lower mi. This will offer the highest
probability for additional convective development for areas mainly
north of I-69 going forward into the evening hours. Precip chances
will be tapered lower accordingly with southward extent. Sufficient
deep layer shear to offer modest organization potential, but with
paltry mid level lapse rates capping prospective convective depth.
Gusty winds and brief heavy downpours with any activity through early
tonight. Model signal exists for some degree of low stratus and/or
fog formation late tonight owing the high near surface moisture
content. Lower confidence yet in defining scale of any development,
as lingering higher based cloud and sufficient low level gradient may
prove disruptive. Introductory mention of patchy fog for late
tonight sufficient at this stage.
Little variation in overall conditions Tuesday. A moist low level
profile will again contribute to weak instability as daytime heating
lifts temperatures into the 70s and maintains a steeper low level lapse
rate environment. MLcape peaking at 700-1000 j/kg. Additional
pockets of dcva projected to work through the existing mid level
trough along the nose of an upper level jet. This occurs as a weak
frontal boundary sags southward into the region. Overall environment
supportive of a chaotic coverage of showers and thunderstorms with a
peak in coverage mid afternoon into the evening hours. Gusty winds
and locally heavy downpours with any stronger cores.
Strong height falls lifting out of the plains will undercut the
great lakes upper low, establishing a deeper, positively upper
trough for the late week period. Some differences across the model
spectrum yet in terms of handling this interaction, but general
expectation exists that sufficient seperation of height falls will
hold the associated surface low and attendant deeper moisture plume
over the Ohio valley as the system pulls east. Local area will
remain suspectible to intervals of showers and thunderstorms tied
closely to daytime heating both Wednesday and Thursday with
continued moist cyclonic flow as the upper low eases through. The
unsettled conditions with prevailing low level easterly flow will
fovor highs near average or slightly below. Drier conditions return
Friday with a window of greater warm air advection lifting
temperatures back above average into the first half of next week.
&&
.MARINE...
An upper level trough is draped over the Great Lakes and will slowly
drop southeast through mid week. Additionally, a warm front up
across the Straits will drop southward through the region on
Tuesday. This will lead to an extended period of unsettled weather
with multiple rounds of showers with occasional embedded
thunderstorms. Pressure gradient is weak and winds aloft are also
weak so chances of any stronger winds or gusts with storms are
lower. Winds will flip from southerly today to northeasterly Tuesday
to which they`ll remain through midweek.
&&
.PREV DISCUSSION...
Issued at 133 PM EDT Mon Sep 22 2025
AVIATION...
A good deal of low level moisture around, as indicated by surface
dew pts well into the 60s across Lower Michigan. This is making for
some chaotic cloud bases, with the northern tafs more embedded in
borderline IFR/MVFR low clouds. Will have chance of renewed
shower/thunderstorm activity late this afternoon over northern tafs,
as thunderstorm complex moving through Lake Michigan will have to be
watched.
Southern tafs are relatively stable, so not expecting
thunderstorms, but still could see some renewed light shower
activity. Winds remain very light through the taf period. As such,
with the amount of surface moisture around, dense fog is a concern
tonight. Good deal of uncertainly with amount of low clouds
around/persisting, with would lessen visibility impacts, and have
gone with a more optimistic IFR/borderline MVFR fog forecast (for
now). Fog gradually burns off tomorrow morning giving way to an
increasing chance of showers/isolated thunderstorm from northwest to
southeast during the day.
For DTW/D21 Convection...
DTW THRESHOLD PROBABILITIES...
* Low for ceilings at or below 5,000 feet, becoming medium late
  tonight.
* Low for cigs/vsby to fall to 200ft and/or 1/2sm late tonight.
* Low for thunderstorms to impact DTW tomorrow afternoon.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&
$$
DISCUSSION...MR
MARINE.......DRK
AVIATION.....SF
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NWS DTX Office Area Forecast Discussion